An elevator is hoisting machinery for conveying passengers and/or freight to different floors by motor-driving an elevator car where the passengers and freight are loaded, the elevator car being connected with a hoist rope having a counterweight on the other end. In such an elevator, an elevator car speed is generally controlled to be constant at a predetermined rated speed, which is referred to as the maximum speed at which a loaded elevator car moves upward.
When selecting a motor that drives an elevator car, a required capacity is calculated from a rated speed predetermined for an elevator car and its maximum laden weight. Then, based on the calculation, such a motor is selected that has enough power to surely drive the elevator car at the rated speed even when the passengers and/or freight are loaded therein to the maximum laden weight. There is disclosed an example of an elevator speed governor that controls an elevator speed depending on its laden weight in Japanese Patent Application Laid-open Publication No. 2004-10335.
However, the elevator car is rather rarely loaded to the maximum laden weight, and in many cases, the car is driven while being loaded to a laden weight lower than the maximum.
In addition, while the load applied to the motor varies depending on the laden weight thereof, a rope weight and friction causing in a sieve or the like cannot be disregarded as a load affecting factor to the motor. Therefore, the elevator car speed cannot be controlled appropriately if the control relies only on the laden weight, as is the case with conventional elevators.